Real or Not Real? An Elevated TSH.

A 19-year-old male presented with mild fatigue and chronic constipation and was found to have an elevated thyroid-stimulating hormone (TSH) level of 85 mIU/L, normal free thyroxine, and normal total triiodothyronine. This presentation was concerning for Macro-TSH, which is rare and may suggest hypothyroidism. This patient's diagnosis of Macro-TSH was confirmed by TSH antibody testing and gel filtration chromatography. We present this case to highlight the need to further evaluate TSH results when thyroid function tests are incompatible with the clinical presentation. Assessment for TSH antibodies, a commercially available test, or gold-standard gel filtration chromatography testing, which is not commercially available, can be used to diagnose Macro-TSH.